Techniques for steering an optical beam

ABSTRACT

Reflectors having concave reflecting surfaces (e.g., parabolic reflectors) and electronically controlled beam steering elements are used for rapid, low-diversion, wide-angle and precision steering of optical beams, including laser beams.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/135,963, which is related to and claims benefit from pendingnon-provisional U.S. patent application Ser. No. 11/392,854, filed Mar.29, 2006, which is herein incorporated by reference, and which wasrelated to and claims the benefit of provisional Patent Application Ser.No. 60/738,771, filed Nov. 22, 2005 (the priority date hereof).

FIELD OF THE INVENTION

The present invention relates to techniques for steering optical beamsand, in particular, laser beams.

BACKGROUND OF THE INVENTION

Precise and controllable delivery of laser beams to a desired locationis required in many communications, industrial, and militaryapplications. Presently, laser beam steering systems typically includeelectro-mechanical systems having massive mirrors, pointing gimbals,turrets, and the like beam steering components. Such systems generallyprovide relatively slow and imprecise beam movements.

SUMMARY OF THE INVENTION

Techniques for steering optical beams are disclosed. Embodiments of theinvention utilize electronically controlled beam steering elements andreflectors having concave reflecting surfaces (e.g., parabolicreflectors) to achieve rapid, low-diversion, wide-angle, and precisionsteering of optical beams, including laser beams.

All objects, features and advantages of the present invention willbecome apparent in the following detailed written description.

The Summary is neither intended nor should it be construed as beingrepresentative of the full extent and scope of the present invention,which these and additional aspects will become more readily apparentfrom the detailed description, particularly when taken together with theappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating ray paths for paraxial raysin a parabolic reflector.

FIG. 1A is a schematic perspective view of a beam steering device havingthe parabolic reflector of FIG. 1.

FIG. 2 is a schematic diagram of a beam steering apparatus having aparabolic reflector, according to one embodiment of the invention.

FIG. 3 is a schematic diagram of a beam steering apparatus having aparabolic reflector, according to another embodiment of the invention.

FIG. 3A is a schematic perspective view of the beam steering apparatusof FIG. 3.

FIG. 4 is a schematic diagram of a beam steering apparatus having twoparabolic reflectors, according to one embodiment of the invention.

FIG. 5 is a schematic diagram of a beam steering apparatus having twoparabolic reflectors, according to another embodiment of the invention.

FIGS. 5A-5B are schematic perspective views of the beam steeringapparatuses of FIGS. 4-5.

FIG. 6 is a schematic diagram of a beam steering apparatus having twooff-axis parabolic reflectors, according to one embodiment of theinvention.

FIG. 6A-6B are schematic perspective views of the beam steeringapparatus of FIG. 6.

FIG. 7 is a schematic diagram of a beam steering apparatus having a flatminor and a parabolic reflector, according to one embodiment of theinvention.

FIG. 8 is a schematic perspective view of the beam steering apparatus ofFIG. 7.

FIG. 9 is another schematic perspective view of the beam steeringapparatus of FIG. 6.

FIG. 9A is still another schematic perspective view of the beam steeringapparatus of FIG. 6.

FIG. 10 is an exemplary polar iso-candela plot of output beams in theapparatus of FIG. 6.

The images in the drawings are simplified for illustrative purposes andare not depicted to scale. To facilitate understanding, identicalreference numerals are used, where possible, to designate substantiallyidentical elements that are common to the figures, except that suffixesmay be added, when appropriate, to differentiate such elements.

It has been contemplated that features or steps of one embodiment may beincorporated in other embodiments of the invention without furtherrecitation.

DETAILED DESCRIPTION

The present invention relates to techniques for steering optical beamsand, in particular, for rapid, low-diversion, wide-angle, and precisionsteering of laser beams, among other optical beams. Herein, the terms“reflector” and “reflecting surface” and the terms “ray,” “beam,”“optical beam,” and “laser beam” are used interchangeably. The term“light” is broadly used in reference to visible and invisibleelectro-magnetic radiation.

Parabolic reflectors of light (i.e., reflectors having concave parabolicreflecting surfaces) are used in the discussed below preferredembodiments of inventive beam steering apparatuses. However, inalternate embodiments of such apparatuses, the parabolic reflectors orat least a portion thereof may be substituted by reflectors having othertypes of concave reflecting surfaces, including spherical, aspherical,cylindrical, ellipsoidal, or hyperboloid reflecting surfaces.

FIG. 1 is a schematic diagram illustrating ray paths for paraxial raysin a parabolic reflector. A narrow beam of light from a reasonablycollimated light source is directed towards a parabolic reflector 12 viaa point u. Conventionally, only beams 14, 15 representing the extremesof a beam steering range in one particular plane are shown. At oneextreme of the beam steeling range, beam 14 passes through the point uat an angle α to an optical axis c-u of the parabolic reflector 12. Thebeam 14 is reflected from the parabolic reflector 12 as a beam 16passing through a point v on the optical axis c-u at an angle α to theoptical axis. Distances c-v and c-u may be calculated from focusingproperties of the parabolic reflector 12 using an equation 1/v+1/u=2/r,where f is a focal length and r is a radius of curvature of theparabolic reflector 12, respectively. At other extreme of the beamsteering range, a beam 15 passing through the point u is then reflectedfrom the parabolic reflector 12 as a beam 17, which passes through thepoint v at an angle β to the optical axis c-u. As such, the parabolicreflector 12 amplifies a steering range of a beam passing through thepoint u from 2α to 2β. However, in this configuration, the parabolicreflector 12 produces diverging output beams (a divergence angle y ofthe beam 16 is shown).

FIG. 1A is a schematic perspective view of a beam steering device havingthe parabolic reflector 12 of FIG. 1. A three-dimensional cone 13emanating from the point v represents a field of regard for opticalbeams, which are originated by a reasonably collimated light source 18(e.g., laser).

FIG. 2 a schematic diagram of a beam steering apparatus having aparabolic reflector, according to one embodiment of the invention. Thebeam steering apparatus includes the light source 18 that emits a beam20, such as a laser beam. Using beam-forming optics, the beam 20 isdirected, via an opening in the parabolic reflector 12, to a small-anglebeam steering element 24 located at the point u. The beam-forming opticsgenerally comprises at least one beam-focusing lens and/orbeam-collimating lens, and other like lens (collectively, shown asfocusing lens 22). In one embodiment, the steering element 24 comprisesa planar mirror controlled by a piezoelectric controller (e.g., S-330piezoelectric controller available from Physik Instrumente (PI) GmbH &Co. KG of Karlsruhe, Germany). In alternate embodiments, the steeringelement 24 may comprise an acousto-optical deflector, amicro-electromechanical systems (MEMS) deflector, an electro-opticaldeflector, and any like beam steering device. After passing through thelens 22, the beam 20 becomes a beam 23 directed, via an opening in theparabolic reflector 12, onto the steering element 24. The steeringelement 24 is positioned at the point u and is aligned to steer the beam23 onto the surface 12. At one end of a steering range, the beam 23 isreflected, as the beam 14, to the surface 12 and, thereafter, as thebeam 16. At the other end of the range, the beam 23 is reflected as thebeam 15 to the parabolic reflector 12 and, thereafter, as the beam 17.In this embodiment, the lens 22 focuses the beam 23 (beams 14 and 15thereof are shown) onto a surface 28. The surface 28 is disposed infront of the surface 12 and intersects, at a boundary of a steeringrange, with a surface 26 that passes through the focal point f and isdisposed parallel to the parabolic reflector 12. Whereas the outputbeams 16 and 17 are well collimated, other output beams in a steeringrange of such beam steering apparatus may posses some residualdivergence.

FIG. 3 is a schematic diagram of a beam steering apparatus having aparabolic reflector, according to another embodiment of the invention.The beam steering apparatus includes the lens 22 focusing the beam 23onto the surface 28, which coincides with the surface 26 and isseparated from the parabolic reflector 12 by a distance r/2, where r isa radius of curvature of the reflector 12. In this embodiment, thesteering element 24 is positioned at a distance 3r/2 from the reflector12, and beams originating by the light source 18 produce well collimatedoutput beams (collimated beam 16 is shown) in an entire steering rangeof the beam steering apparatus.

FIG. 3A is a schematic perspective view of the beam steering apparatusof FIG. 3. In one exemplary embodiment, in an arbitrary plane 11,divergence of the output laser beams is ½ micro-radian or less within asteering range of about +/−6 degrees.

FIG. 4 is a schematic diagram of a beam steering apparatus having twoparabolic reflectors, according to one embodiment of the invention. Inthis embodiment, the lens 22 and a parabolic reflector 30 focus opticalbeams originated by the light source 18 onto the coinciding surfaces 26and 28, which are parallel to the parabolic reflector 12 and aredisposed at the focal length f from thereof. The beam steering apparatusalso includes the steering element 24 and the parabolic reflector 12.After leaving the lens 22, the beam 23 is directed, by the steeringelement 24 through an opening in the parabolic reflector 12, to theparabolic reflector 30. Beams reflected from the parabolic reflector 30pass through the point u disposed at a distance 3r/2 from the parabolicreflector 12 and are focused onto the surfaces 26/28 passing through thefocal point f separated from the parabolic reflector 12 by a distancer/2, where r is a radius of curvature of the reflector 12. In operation,the parabolic reflector 30 amplifies a steering range that might beachieved by using only the parabolic reflector 12 (discussed inreference to FIGS. 3-3A).

FIG. 5 is a schematic diagram of a beam steering apparatus having twoparabolic reflectors, according to another embodiment of the invention.In this embodiment, the lens 22 and parabolic reflector 30 focus opticalbeams originated by the light source 18 onto a surface 27, which isdisposed in front of and parallel to the parabolic reflector 30. Adistance between the surface 27 and the parabolic reflector 30 isselected such that a beam focused onto the surface 27 is then focused,by the parabolic reflector 30, onto the coinciding surfaces 26/28(discussed above in reference to FIG. 4).

FIGS. 5A-5B are schematic perspective views of the beam steeringapparatuses of FIGS. 4-5. In exemplary embodiments, values of factors ofamplification of the parabolic reflectors 12 and 30 are about 2-4 and10-30, respectively. In exemplary embodiments, an output steering rangeof such beam steering apparatuses may be about +/−30-45 degrees orgreater. However, as shown in FIG. 5B, in some embodiments, the outputsteering range may partially be obstructed by the parabolic reflector 30(obstructed field 31 is shown).

FIG. 6 is a schematic diagram of a beam steering apparatus having twooff-axis parabolic reflectors, according to one embodiment of theinvention. In contrast with the steering apparatuses of FIGS. 4-5,optical axes of the parabolic reflectors 12 and 30 are disposed in thesame plane, however, in an angular/spatial relationship providingelimination of obstruction of an output steering range of the apparatusby the parabolic reflector 30 thereof. In particular, optical axes ofthe parabolic reflectors 12 and 30 are disposed at pre-determined anglesto one another and to the reflecting surface of the steering element 24,while a ray focusing scheme of the beam steering apparatus maycorrespond to one discussed in reference to FIG. 5 (as shown) or,alternatively, in reference to FIG. 4.

FIGS. 6A-6B are schematic perspective views of the beam steeringapparatus of FIG. 6. An output steering range 13 of such an apparatus isfree from obstruction caused by the parabolic reflector 30 and may beabout +/−30-45 degrees or greater.

FIG. 7 is a schematic diagram of a beam steering apparatus having a flatmirror and a parabolic reflector, according to one embodiment of theinvention. The beam steering apparatus generally comprises the lightsource 18, a collimating lens 38, a beam-forming optics including afirst beam expander lens 40, a second beam expander lens 42, and afocusing lens 44, an electrically controllable steering platform 32having the steering element 24, a flat mirror 34, and the parabolicreflector 12. A laser beam 36 from the light source 18 (not shown)passes through the collimating lens 38 to the first beam expander lens40. The lens 40 focuses the incident beam onto a focal point thereof(not shown) shared with the second beam expander lens 42, which directsthe expanded and collimated laser beam towards the focusing lens 44. Thefocusing lens 44 directs the beam to the steering element 24. Thesteering element 24 reflects the beam onto the flat minor 34, which isaligned for re-directing the beam towards the parabolic reflector 12.source 18 is situated at coordinates (0, 37, 42) mm, while the lens 22having a focal length of 150 mm and a diameter of 25 mm is situated atcoordinates (0, 28, 9) mm. The steering element 24 has a steering rangeof approximately +/−1.5 degrees and is situated at coordinates (0, 8,−60) mm, and a distance between the steering element 24 and lens 22 isabout 72 mm. The parabolic reflector 30 has a focal length of 20 mm andis situated at coordinates (0,0,40), so that a distance between theparabolic reflector 30 and steering element 24 is about 100 mm. Theparabolic reflector 12 has a focal length of 20 mm and is situated atcoordinates (0, −33, −58) mm, and a distance between the parabolicreflectors 12 and 30 is about 103 mm. An output steering range of thebeam steering apparatus is about +/−30-45 degrees, a frequency of beamscanning is about 1 KHz, and a pointing accuracy is about 1micro-radian.

FIG. 9A is still another schematic perspective view of the beam steeringapparatus of FIG. 6, wherein a plurality of beams originated from thelight source 18 is depicted to illustrate a three-dimensional pattern ofray paths formed in a steering range of the apparatus.

FIG. 10 is an exemplary polar iso-candela plot of output beams in theapparatus of FIG. 6. The plot depicts, in polar coordinates, aconstant-power profile of a large number of output beams for theembodiment discussed in reference to FIG. 9. The plot shows that anangular range of the output beam has a profile of a slightly flattenedcone, which subtends about +/−45 degrees and +/−50 degrees alongorthogonal axes. The plot indicates that there are no “blind” spots(i.e., no obstructions) in the steering range, and that the output beamsare substantially uniform.

One of ordinary skill in the art will realize that other opticalarrangements for beam-forming and/or beam-focusing optics may be used inplace of or in addition to the described configurations withoutdeparting from the concepts of the invention. Particular optical designsmay be completed using, for example, the TracePro™ program availablefrom Lambda Research, Inc. of Littleton, Mass., and the like softwareproducts.

Although the invention herein has been described with reference toparticular illustrative embodiments thereof, it is, to be understoodthat these embodiments are merely illustrative of the principles andapplications of the present invention. Therefore numerous modificationsmay be made to the illustrative embodiments and other arrangements maybe devised without departing from the spirit and scope of the presentinvention, which is defined by the appended claims.

What is claimed is:
 1. An apparatus for steering an optical beam, theapparatus comprising: a first reflector provided with a first concavereflecting surface (CRS) having a first focal length and a first opticalaxis; a second reflector provided with a second CRS having a secondfocal length and a second optical axis; a beam steering element having aflat reflective surface; and a beam-forming for focusing the opticalbeam onto said beam steering element; wherein said beam steering elementis aligned for reflecting the optical beam directly onto the second CRSand said second CRS is aligned for reflecting the optical beam directlyonto said first CRS; and further wherein the distance between said firstreflector and said second reflector is at least three times the focallength of said first reflector.
 2. The apparatus of claim 1, wherein atleast one of the first CRS and the second CRS is a spherical reflectingsurface, an aspherical reflecting surface, a cylindrical reflectingsurface, an ellipsoidal reflecting surface, a parabolic reflectingsurface or a hyperboloidal reflecting surface.
 3. The apparatus of claim1, wherein the optical beam, after being reflected by said second CRS,passes through a point disposed at a distance of three times the focallength of said first CRS, and is focused onto a first surface disposedin front of said first CRS which is parallel to said first CRS andpasses through a focal point of said first CRS.
 4. The apparatus ofclaim 3, wherein the beam-forming optics focuses the first beam onto asecond surface parallel to and disposed in front of said second CRS,wherein the distance between said second CRS and said second surface isselected such that when said optical beam is focused onto said secondsurface by said beam forming optics it is also focused by said secondCRS onto said first surface.
 5. The apparatus of claim 4, wherein theoptical beam reflected from the second CRS intersects an optical axisthereof a distance from the first CRS equal to 3 times the first focallength.
 6. The apparatus of claim 1, wherein the first optical axiscoincides with the second optical axis.
 7. The apparatus of claim 1,wherein the first optical axis is disposed at an angle to the secondoptical axis.
 8. The apparatus of claim 7, wherein the first opticalaxis and the second optical axis are disposed in one plane.
 9. Theapparatus of claim 7, wherein the first optical axis, the second opticalaxis, and an optical axis of the beam-forming optics are disposed in oneplane.
 10. The apparatus of claim 1, wherein the first beam propagatesfrom the beam steering element towards the second CRS though an openingin the first CRS.
 11. The apparatus of claim 1, wherein the beamsteering element is an electronically controlled beam steering element.12. The apparatus of claim 11, wherein the electronically controlledbeam steering element is a piezoelectric beam steering element.
 13. Theapparatus of claim 1, wherein said angle between said first optical axisand said second optical axis and the angle between said second opticalaxis and the reflecting surface of said beam steering element areselected to provide elimination of obstruction of the output steeringrange by said second reflector.
 14. The apparatus of claim 1, whereinthe beam-forming optics comprises at least one beam-focusing lens orbeam-collimating lens.
 15. A method for steering an optical beam, themethod comprising: directing the optical beam onto a beam steeringelement having a flat reflective surface; directing the optical beamreflected from the beam steering element directly onto a first concavereflecting surface (CRS) having a first focal length and a first opticalaxis; directing the optical beam reflected from the first CRS directlyonto a second CRS forming an output beam; and engaging the beam steeringelement to steer the output beam; wherein the distance between saidfirst CRS and said second CRS is at least three times the focal lengthof said first CRS.
 16. The method of claim 15, wherein at least one ofthe first CRS and the second CRS is a spherical reflecting surface, anaspherical reflecting surface, a cylindrical reflecting surface, anellipsoidal reflecting surface, a parabolic reflecting surface or ahyperboloidal reflecting surface.
 17. The method of claim 15, furthercomprising: directing the optical beam towards the first CRS though anopening in the second CRS.
 18. The method of claim 15, furthercomprising: focusing the optical beam onto a first surface disposed infront of the first CRS said first surface being (i) parallel to saidfirst CRS and (ii) passing through a focal point of said first CRS. 19.The method of claim 18, further comprising: focusing the first beam ontoa second surface parallel to and disposed in front of said second CRS,wherein the distance between said second CRS and said second surface isselected such that when said optical beam is focused onto said secondsurface by said beam forming optics it is also focused by said secondCRS onto said first surface.